1 . Field of the Invention
This invention relates to a current sensing relay and, more specifically, to a plural pole relay for magnetically opening a normally closed switch of a circuit upon sensing of a predetermined electrical current.
2 . Brief Description of the Prior Art
In accordance with the prior art, filament windings of fluorescent lamps and the like remain in an energized state after lighting of the lamp since there is no provision for cutting off the filament current after commencement of lamp operation. This condition results in waste of energy as well as production of possibly unwanted heat which also must be dissipated in some manner. The prior art has attempted to alleviate this problem in several ways, such as by the use of timers in the filament circuits to cut off current to the filaments after a predetermined period of time. Other solutions to the problem are shown in Latassa (U.S. Pat. No. 4,009,412) where there is provided a secondary winding supply lamp current and a tertiary winding to supply heater current wherein a magnetic switch is provided which senses current through the secondary winding and opens the heater current circuit in response thereto. Other prior art of this type is shown in Feinberg (U.S. Pat. No. 4,568,860), Citino (U.S. Pat. No. 4,661,745), Fuller (U.S. Pat. No. 4,559,478), Regan (U.S. Pat. No. 4,339,690), Morton (U.S. Pat. No. 4,082,981) and Powell (U.S. Pat. No. 3,866,087). These prior art solutions have been subject to one or more of several problems, these including cost, the use of normally open switches wherein the switch must close to ignite the lamps initially and switch failure therefore results in fixture lighting failure. These problems have been overcome in opending application Ser. No. 07/454,592, assigned to the assignee of the present invention, in which there are disclosed and claimed several embodiments of a simple and relatively inexpensive normally closed device to cut off filament current to all starting filaments in fluorescent lamps and the like shortly after commencement of lamp operation. In that application a three pole relay is disclosed which operates in response to the flow of normal operating current across a fluorescent lamp device to energize a coil, the coil actuating the relay to open switches disposed in all of the filament lines associated with the lamps to shut off filament current while maintaining current flow across the lamp itself. In one such embodiment there is provided a can of magnetic material to which is crimped a cover of non-magnetic material to form an enclosure within the can. A coil is disposed within the can, thereagainst at one end thereof and around a center post of magnetic material. A plastic flange optionally having a shorting turn therein is secured to the other end of the coil. Also positioned within the can and abutting the interior end of the center post is a steel coin which is secured to a plastic disc. The coin/disc and plastic flange are normally biased apart by a compression spring. The center post, can and steel coin form a magnetic circuit whereby, when the coil is energized, the coin is attracted toward the coil and against the bias of the spring. A plurality of normally closed switches are maintained in the closed position by the plastic actuator when the disc is in its normal position. Upon energization of the coil, with the steel coin and plastic actuator being attracted toward the coil and away from the switches, the switches are opened to open circuits in which these switches are connected.
The switches are mounted on the cover which is formed of non-magnetic material such as plastic each of which comprises a thin flexible elongated contact blade attached at one end to the cover by a terminal which passes through a bore in the cover. The blade is adapted to move into and out of engagement with another terminal member which passes through another bore in the cover. A typical mounting of the contact blades sandwich the blade between a terminal lead and the plastic cover. The electrical quality of the type of joint is dependent upon the compression of the blade and the resiliency of the plastic which tends to cold flow over time. Compression joints are also susceptible to variations in assembly forces, plastic cold flow and rough handling which can result in a high resistance connection or a loose blade.
It is an object of the invention to provide a mounting for the contact blade which has improved reliability and which is easily assembled, inexpensive and yet one possessing low, stable electrical resistance with good retention force with the plastic cover. Another object is to provide such a mounting that is effectively impervious to contamination and environmental conditions. Yet another object is the provision of a mounting system for the elongated movable blade that has superior anti-rotational characteristics.